Total gestation lasts 11 to 11.5 months.
Scientists are reasonably certain that California sea lions have delayed implantation: when the fertilized egg divides into a hollow ball of cells one layer thick (blastocyst) it stops growing and floats freely in the uterus for about three months. The blastocyst then implants in the uterine wall and continues to develop. A study of California sea lions in zoological habitats showed that blastocyst implantation appears to be triggered by day length. Delayed implantation assures that the pup will be born when environmental conditions are optimal for its survival.
Pupping (Birth) Season
Most California sea lion pups are born in June. Galápagos sea lion pups are born throughout most of the year, probably because of the year-round warm, tropical climate. Peak season is late May to January.
Frequency of Birth
Females generally give birth to one pup each year. Multiple births have never been observed in the wild. In zoological habitats however, twins have been documented.
Pups are born on land.
Pupping may last from a few minutes to an hour. Approximately 63% of pups are delivered head-first.
The female vocalizes often during and immediately after the birth of her pup. The pup instinctively replies. This vocal interaction may continue for 20 minutes or more. This helps establish the mother-pup bond. The female may also smell, nuzzle, pull, and nip at her pup.
Pup at Birth
Pups are about 75 cm (29.6 in.) and 6 kg (13.2 lbs.).
Pups are dark chocolate brown to black at birth. They undergo two molts in the first six months.
Pups are well developed at birth. They are born with their eyes open and can vocalize. Within 30 minutes they are able to shake, groom, scratch, and walk. Pups appear to be able to swim at birth, although their movements are not well coordinated.
Care of Young
- All sea lions employ a foraging strategy when nursing. After a few days with her newborn pup, the mother leaves the pup alone while she forages at sea. Having replenished her energy reserves, she returns and nurses her pup again. As the pup grows she leaves for progressively longer foraging trips.
- Pups suck vigorously and can actually be heard several meters away.
- For the first two months of nursing a new pup, a mother sea lion's milk contains 32% fat, about 9% protein, and 0.6% lactose (milk sugar). By the fourth month of nursing, the fat content may increase to 44%. The protein and lactose remain relatively constant.
- Nursing normally continues for six to twelve months, although females have frequently been observed nursing yearlings. These findings are compatible with observations of California sea lions in zoological habitats. Some Galápagos sea lions have been documented nursing as long as three years.
- In addition to nursing, pups begin eating fish at about two months.
- Under most circumstances, a female will nurse only her own pup. Fostering behavior has been observed, but is not as common as in some other pinnipeds.
- A female is very protective of her pup for the first two to four days. Aggressive, almost territorial displays and open-mouth threats to other females are common.
- Female and pup recognize each other through a series of standard behaviors. As soon as a female returns to the rookery from foraging she vocalizes repeatedly. More than one pup may respond, so she makes her final identification by smelling her own pup. Vocal cues may be the most important factor in mother-pup recognition. A recent study found that a female will leave her pup to move toward a taped recording of her pup's vocals.
- Researchers have observed Galápagos sea lions grooming their pups. Grooming has not been observed in the California subspecies.
Pup Growth and Development
Pups learn by mimicking adult behavior.
Pups begin to group together at two to three weeks of age. Pups develop vocal, social, and swimming skills by interacting with others in these groups. These social groups break up by the end of the breeding season when the adults leave the rookery.
Research on California sea lions in zoological habitats suggests that mothers and juveniles recognize each other after weaning and may continue to associate with each other.